Planetary nomenclature, like terrestrial nomenclature, is a system of uniquely identifying features on the surface of a planet or natural satellite so that the features can be easily located, described, and discussed. The task of assigning official names to features is taken up by the International Astronomical Union since its founding in 1919. [1]
When images are first obtained of the surface of a planet or satellite, a theme for naming features is chosen and a few important features are named, usually by members of the appropriate IAU task group (a commonly accepted planet-naming group). Later, as higher resolution images and maps become available, additional features are named at the request of investigators mapping or describing specific surfaces, features, or geologic formations. Anyone may suggest that a specific name be considered by a task group. If the members of the task group agree that the name is appropriate, it can be retained for use when there is a request from a member of the scientific community that a specific feature be named. Names successfully reviewed by a task group are submitted to the IAU Working Group for Planetary System Nomenclature (WGPSN). Upon successful review by the members of the WGPSN, names are considered provisionally approved and can be used on maps and in publications as long as the provisional status is clearly stated. Provisional names are then presented for adoption to the IAU's General Assembly, which met triennially in the past, and which now adopts nomenclature for planetary surface features as required. A name is not considered to be official — that is, "adopted" — until the General Assembly has given its approval.
Names adopted by the IAU must follow various rules and conventions established and amended through the years by the Union. These include:
In addition to these general rules, each task group develops additional conventions as it formulates an interesting and meaningful nomenclature for individual planetary bodies.
Names for all planetary features include a descriptor term, with the exception of two feature types. For craters, the descriptor term is implicit. Some features named on Io and Triton do not carry a descriptor term because they are ephemeral.
In general, the naming convention for a feature type remains the same regardless of its size. Exceptions to this rule are valleys and craters on Mars and Venus; naming conventions for these features differ according to size.
One feature classification, regio, was originally used on early maps of the Moon and Mercury (drawn from telescopic observations) to describe vague albedo features. It is now used to delineate a broad geographic region.
Named features on bodies so small that coordinates have not yet been determined are identified on drawings of the body that are included in the IAU Transactions volume of the year when the names were adopted. Satellite rings and gaps in the rings are named for scientists who have studied these features; drawings that show these names are also included in the pertinent Transactions volume. Names for atmospheric features are informal at present; a formal system will be chosen in the future.
The boundaries of many large features (such as terrae, regiones, planitiae and plana) are not topographically or geomorphically distinct; the coordinates of these features are identified from an arbitrarily chosen center point. Boundaries (and thus coordinates) may be determined more accurately from geochemical and geophysical data obtained by future missions.
| Feature | Description | Designation |
|---|---|---|
| Albedo feature | An area which shows a contrast in brightness or darkness (albedo) with adjacent areas. This term is implicit. | AL |
| Arcus, arcūs | Arc: curved feature | AR |
| Astrum, astra | Radial-patterned features on Venus | AS |
| Catena, catenae | A chain of craters e.g. Enki Catena. | CA |
| Cavus, cavi | Hollows, irregular steep-sided depressions usually in arrays or clusters | CB |
| Chaos | A distinctive area of broken or jumbled terrain e.g. Iani Chaos. | CH |
| Chasma, chasmata | Deep, elongated, steep-sided depression e.g. Eos Chasma. | CM |
| Colles | A collection of small hills or knobs. | CO |
| Corona, coronae | An oval feature. Used only on Venus and Miranda. | CR |
| Crater, craters | A circular depression likely created by impact event. This term is implicit. | AA |
| Dorsum, dorsa | Ridge, sometimes called a wrinkle ridge e.g. Dorsum Buckland. | DO |
| Eruptive center | An active volcano on Io. This term is implicit. | ER |
| Facula, faculae | Bright spot | FA |
| Farrum, farra | Pancake-like structure, or a row of such structures | FR |
| Flexus, flexūs | Very low curvilinear ridge with a scalloped pattern | FE |
| Fluctus, fluctūs | Terrain covered by outflow from a volcano. | FL |
| Flumen, flumina | Channel on Titan that might carry liquid | FM |
| Fossa, fossae | Long, narrow, shallow depression | FO |
| Insula, insulae | Island (islands), an isolated land area (or group of such areas) surrounded by, or nearly surrounded by, a liquid area (sea or lake). The only feature with this designation is Mayda Insula. | IN |
| Labes, labēs | Landslide debris. Used only on Mars. | LA |
| Labyrinthus, labyrinthi | Complex of intersecting valleys or ridges. | LB |
| Lacus | A "lake" or small plain. Used on the Moon, Mars and Titan. | LC |
| Landing site name | Lunar features at or near Apollo landing sites | LF |
| Large ringed feature | Cryptic ringed features | LG |
| Lenticula, lenticulae | Small dark spots on Europa | LE |
| Linea, lineae | Dark or bright elongate marking, may be curved or straight | LI |
| Macula, maculae | Dark spot, may be irregular | MA |
| Mare, maria | A "sea" or large circular plain e.g. Mare Erythraeum. Used on the Moon, Mars and Titan. | ME |
| Mensa, mensae | A flat-topped prominence with cliff-like edges, i.e. a mesa. | MN |
| Mons, montes | Mons refers to a mountain. Montes refers to a mountain range. | MO |
| Oceanus | Very large dark area. Used only on the Moon. | OC |
| Palus, paludes | "Swamp"; small plain. Used on the Moon and Mars. | PA |
| Patera, paterae | Irregular crater, or a complex one with scalloped edges e.g. Ah Peku Patera. Usually refers to the dish-shaped depression atop a volcano. | PE |
| Planitia, planitiae | Low plain e.g. Amazonis Planitia. | PL |
| Planum, plana | A plateau or high plain e.g. Planum Boreum. | PM |
| Plume | A cryovolcanic feature on Triton. This term is currently unused. | PU |
| Promontorium, promontoria | "Cape"; headland. Used only on the Moon. | PR |
| Regio, regiones | Large area marked by reflectivity or color distinctions from adjacent areas, or a broad geographic region | RE |
| Reticulum, reticula | reticular (netlike) pattern on Venus | RT |
| Rima, rimae | Fissure. Used only on the Moon. | RI |
| Rupes, rupēes | Scarp | RU |
| Satellite feature | A feature that shares the name of an associated feature, for example Hertzsprung D. | SF |
| Scopulus, scopuli | Lobate or irregular scarp | SC |
| Sinus | "Bay"; small plain e.g. Sinus Meridiani. | SI |
| Sulcus, sulci | Subparallel furrows and ridges | SU |
| Terra, terrae | Extensive land mass e.g. Arabia Terra. | TA |
| Tessera, tesserae | An area of tile-like, polygonal terrain. This term is used only on Venus. | TE |
| Tholus, tholi | Small domical mountain or hill e.g. Hecates Tholus. | TH |
| Undae | A field of dunes. | UN |
| Vallis, valles | A valley e.g. Valles Marineris. | VA |
| Vastitas, vastitates | An extensive plain. The only feature with this designation is Vastitas Borealis. | VS |
| Virga, virgae | A streak or stripe of color | VI |
| Feature type | Current list | Naming convention |
|---|---|---|
| Craters | list [1] | Famous deceased artists, musicians, painters, authors |
| Dorsa | list [2] | Astronomers who made detailed studies of the planet |
| Fossae | list [3] | Significant works of architecture |
| Montes | list [4] | Words for "hot" in various languages. Only one mountain is currently named: Caloris Montes, from Latin word for "heat" |
| Planitiae | list [5] | Names for Mercury (either planet or god) in various languages |
| Rupēs | list [6] | Ships of discovery or scientific expeditions |
| Valles | list [7] | Radio telescope facilities |
All but three features on Venus are named after females. These three exceptions were named before the convention was adopted, being respectively Alpha Regio, Beta Regio, and Maxwell Montes which is named after James Clark Maxwell
| Feature type | Current list | Naming convention |
|---|---|---|
| Astra | none [8] | Goddesses, miscellaneous |
| Chasmata | list [9] | Goddesses of hunt; moon goddesses |
| Colles | list [10] | Sea goddesses |
| Coronae | list [11] | Fertility and earth goddesses |
| Craters | list [12] | Over 20 km; famous women; under 20 km, common female first names |
| Dorsa | list [13] | Sky goddesses |
| Farra | list [14] | Water goddesses |
| Fluctūs | list [15] | Goddesses, miscellaneous |
| Fossae | list [16] | Goddesses of war |
| Labyrinthi | list [17] | Goddesses, miscellaneous |
| Lineae | list [18] | Goddesses of war |
| Montes | list [19] | Goddesses, miscellaneous (also one radar scientist) |
| Paterae | list [20] | Famous women |
| Planitiae | list [21] | Mythological heroines |
| Plana | list [22] | Goddesses of prosperity |
| Regiones | list [23] | Giantesses and Titanesses (also two Greek alphanumeric) |
| Rupēs | list [24] | Goddesses of hearth and home |
| Terrae | list [25] | Goddesses of love |
| Tesserae | list [26] | Goddesses of fate and fortune |
| Tholi | list [27] | Goddesses, miscellaneous |
| Undae | list [28] | Desert goddesses |
| Valles | list [29] | Word for planet Venus in various world languages (400 km and longer); river goddesses (less than 400 km in length) |
| Feature type | Naming convention |
|---|---|
| Craters | Craters are generally named after deceased scientists, scholars, artists and explorers who have made outstanding or fundamental contributions to their field. Additionally, craters in or around Mare Moscoviense are named after deceased Russian cosmonauts and craters in and around Apollo crater are named after deceased American astronauts (see Space accidents and incidents). This convention may be extended if other space-faring countries suffer fatalities in spaceflight. |
| Lacūs, Maria, Paludes, Sinūs | These features are assigned names which are Latin terms describing weather and other abstract concepts. |
| Montes | Montes are named after terrestrial mountain ranges or nearby craters. |
| Rupēs | Rupēs are named after nearby mountain ranges (see above). |
| Valles | Valles are named after nearby features. |
| Others | Features that don't fall into any of the above categories are named after nearby craters. |
| Feature type | Naming convention |
|---|---|
| Large craters | Deceased scientists who have contributed to the study of Mars; writers and others who have contributed to the lore of Mars |
| Small craters | Villages of the world with a population of less than 100,000. |
| Large valles | Name for Mars/star in various languages |
| Small valles | Classical or modern names of rivers |
| Other features | From nearest named albedo feature on Schiaparelli or Antoniadi maps. See Classical albedo features on Mars for a list. |
When space probes have landed on Mars, individual small features such as rocks, dunes, and hollows have often been given informal names. Many of these are frivolous: features have been named after ice cream (such as Cookies N Cream); cartoon characters (such as SpongeBob SquarePants and Patrick); and '70s music acts (such as ABBA and the Bee Gees).[2]
Features on Deimos are named after authors who wrote about Martian satellites. There are currently two named features on Deimos - Swift crater and Voltaire crater - after Jonathan Swift and Voltaire who predicted the presence of Martian moons.
All features on Phobos are named after scientists involved with the discovery, dynamics, or properties of the Martian satellites or people and places from Jonathan Swift's Gulliver's Travels.
People and places associated with the Amalthea myth
Features on Thebe are named after people and places associated with the Thebe myth. There is only one named feature on Thebes - Zethus crater.
| Feature type | Naming convention |
|---|---|
| Active eruptive centers | Active volcanoes on Io are named after fire, sun or thunder gods or heroes. |
| Catenae | Crater chains are named after Sun gods. |
| Fluctūs | Names of fluctūs are derived from a nearby named feature, fire, sun, thunder or volcano gods, goddesses and heroes or mythical blacksmiths. |
| Mensae, Montes, Plana, Regiones and Tholi | These features can be named after places associated with Io mythology, derived from nearby named features, or places from Dante's Inferno |
| Paterae | Paterae on Io are named after fire, sun, thunder or volcano gods, heroes or goddesses or mythical blacksmiths. |
| Valles | Names of valleys are derived from nearby named features. |
| Feature type | Naming convention |
|---|---|
| Chaos | Places associated with Celtic myths |
| Craters | Celtic gods and heroes |
| Flexūs | Places associated with the Europa myth |
| Large ringed features | Celtic stone circles |
| Lenticulae | Celtic gods and heroes |
| Lineae | People associated with the Europa myth |
| Maculae | Places associated with the Europa myth |
| Regiones | Places associated with Celtic myths |
| Feature type | Naming convention |
|---|---|
| Catenae, craters | Gods and heroes of ancient Fertile Crescent people |
| Faculae | Places associated with Egyptian myths |
| Fossae | Gods (or principals) of ancient Fertile Crescent people |
| Paterae | Paterae on Ganymede are named after wadis in the Fertile Crescent. |
| Regiones | Astronomers who discovered Jovian satellites |
| Sulci | Places associated with myths of ancient people |
| Feature type | Naming convention |
|---|---|
| Large ringed features | Homes of the gods and of heroes |
| Craters | Heroes and heroines from northern myths |
| Catenae | Mythological places in high latitudes |
People from myth of Castor and Pollux (twins)
People from myth of Castor and Pollux (twins)
People and places from Malory's Le Morte d'Arthur legends (Baines translation)
People and places from Burton's Arabian Nights
People and places from Homer's Odyssey
People and places from Virgil's Aeneid
People and places from creation myths
| Feature type | Naming convention |
|---|---|
| Major bright albedo features | Sacred or enchanted places from legends, myths, stories, and poems of cultures from around the world |
| Major dark albedo features | Legendary/mythical primordial seas or enchanted waters from world cultures |
| Craters (and lakes if present) | Lakes from all continents on Earth |
| Fluvial channels | Rivers from all continents on Earth |
| Other features | Deities of happiness, peace, and harmony from world cultures |
Sun and Moon deities
People and places from Sayers' translation of Chanson de Roland
| Feature type | Naming convention |
|---|---|
| Craters | Craters of Phoebe are named after people associated with Phoebe or people from Argonautica by Apollonius Rhodius or Gaius Valerius Flaccus. |
| Other | Non-crater features on Phoebe are named after places from Argonautica. |
Mischievous (Pucklike) spirits (class)
Characters, places from Shakespeare's plays
Light spirits (individual and class)
Dark spirits (individual)
Female Shakespearean characters, places
Shakespearean tragic heroes and places
There are currently no named features on Uranian small satellites, however the naming convention is heroines from plays by Shakespeare and Pope.
Features on Proteus are to be named after water-related spirits, gods or goddesses who are neither Greek nor Roman. The only named feature on Proteus is Pharos.
Geological features on Triton should be assigned aquatic names, excluding those which are Roman and Greek in origin. Possible themes for individual descriptor terms include worldwide aquatic spirits, famous terrestrial fountains or fountain locations, terrestrial aquatic features, famous terrestrial geysers or geyser locations and terrestrial islands.
There are currently no named features on Nereid. When features are discovered, they are to be named after individual nereids.
Features on other satellites of Neptune, once discovered, should be named after gods and goddesses associated with Neptune/Poseidon mythology or generic mythological aquatic beings.
There are currently no named features on Pluto because it is extremely difficult to resolve surface features with current telescopes.[3][4] When discovered, either by telescopic observation or the New Horizons flyby in 2015, Plutonian surface features are to be named after underworld deities.
| Feature type | Naming convention |
|---|---|
| Craters | Caverns and grottos of the world |
| Dorsa | Galileo project participants |
| Regiones | Discoverer of Ida and places associated with the discoverer |
| Feature type | Naming convention |
|---|---|
| Craters | Idaean dactyls |
| Feature type | Naming convention |
|---|---|
| Craters | Spas of the world |
| Regiones | Discoverer of Gaspra, and Galileo project participants |
| Feature type | Naming convention |
|---|---|
| Craters | Coal fields and basins of the world |
| Feature type | Naming convention |
|---|---|
| Craters | Mythological and legendary names of an erotic nature |
| Regiones | Discoverers of Eros |
| Dorsa | Scientists who have contributed to the exploration and study of Eros |
The IAU has named craters and regiones on Itokawa but has not disclosed any naming conventions. [5][6]